Police have released more information about a fiery fatal crash Monday afternoon that left a 61-year-old man dead and snarled traffic for hours on U.S. 59 in southwest Houston.

The wreck happened about 3 p.m. on the outbound Southwest Freeway near Chimney Rock, according to the Houston Police Department.

The freeway was shut down following the crash and the lanes did not reopen until about 11:40 p.m. after the charred and crumpled vehicles were hauled away and the scene was cleared.

Police said the driver of a red Jeep Cherokee was driving erratically when he hit a U.S. Postal Service big-rig. Both the Jeep and 18-wheeler slammed into a concrete wall. The Jeep was pinned against the wall as the two vehicles slid along the barrier.

U.S. Postal Service officials said the truck was empty at the time of the crash. The driver was an employee of the Postal Service and has since been released from the hospital.

Police are still investigating the wreck.

The freeway shutdown caused traffic headaches as drivers sought alternate routes to avoid the crash site. Streets and other freeways were crowded.

"Anytime you have traffic tie ups on a freeway, it's going to affect other traffic routes," said Victor Senties, a spokesman for the Houston Police Department.

Senties said the length of crash investigations may vary, depending upon the wrecks.

There were no reports of serious traffic congestion because drivers diverted to routes away from the wreck, but it's not uncommon for roadways to become jammed in such situations, said Dinah Massie, spokeswoman for Houston TranStar.

Monday's crash required the Department of Transportation to inspect the freeway barrier to make sure it was safe before the road could be reopened, said Danny Perez, a department spokesman. Also, Perez added, a fuel spill at the scene had to be cleaned up.

Perez said the investigation was likely further complicated because a federal vehicle was involved the wreck.